Heretofore, surface acoustic waves (SAWs) have been used for frequency synthesizers over BAWs due to their frequency tuning capability. That is, in general, SAWs can be "pulled" in frequency further than BAW resonators. Because of this, they are preferred sources for FM, FSK, and spread-spectrum operations. For FFH (fast frequency hopping) synthesizers, they are also used for the same reason. SAWs are deficient however in their noise properties and stability close to the carrier frequency.